Mast cells play a central role in chronic allergies, asthma, cancer, and skin fibrosis, as well as in bacteria and helminth infections. Recent studies also have implicated these effecter cells in HIV-1 infections and multiple sclerosis. The fourth International Workshop on Signal Transduction in the Activation and Development of Mast Cells and Basophils will be an intense scientific meeting focusing on the latest basic research earned on the mast cell and its related cell the basophil. The specific goals of the Workshop are (1) to present recent advances relating to the factors and mechanisms that regulate the growth, differentiation, and function of mast cells and basophils, (2) to discuss new technological advances that directly impact studies on mast cells and basophils, and (3) to integrate the basic science findings in the framework of therapeutic potential and treatment of diseases such as allergic inflammation which are mediated, in part, by these granulocytes. The Workshop's format will include seven Symposia, two Poster Sessions, and three Keynote Lectures. Drs. William Paul, Joseph Schlessinger, and Reuben Siraganian will give the Keynote Lectures. There will be 44 presentations in the seven Symposia. All presenters are leading authorities on specific aspects of the mast cell and/or basophil. Only cutting edge research will be presented at the Workshop. Moreover, an emphasis will be placed on the use of molecular approaches to address specific aspects of mast cell and basophil development and function. Symposia I will focus on the development of mast cells and basophils. Symposia II and III focus on early and late events in IgE/antigen-mediated activation of mast cells and basophils, respectively. Symposia IV will focus on the mechanisms of exocytosis. Symposia V will focus on non-IgE mediated activation of mast cells and basophils, as well as on those surface receptors that dampen activation responses. Symposia VI will focus on some of the mediators released from activated mast cells and basophils. Finally, Symposia VII will focus on the bilateral interactions of mast cells with other cell types. Recent data relating to the role of mast cells and/or basophils in multiple sclerosis and HIV-1 infection also will be presented in Symposia VII.